Cameras known as "solid sensor cameras" normally comprise a photosensitive matrix covered by a trichrome matrix filter, the arrangement being such that each element of the matrix is assigned to only one single color.
The signals detected at each spot of the matrix are often collected by charge coupling registers CCD. A CCD register is analog to a shift register, but, furthermore, in each of the compartments it stores the amplitude of the signal.
By reason of the large number of points or spots of a photosensitive matrix, it is not possible to collect all the signals by using a single CCD register. This is the reason why two CCD registers are normally used, the first collecting the signals corresponding to the spots of the uneven rank of a line and the second collecting the spots of the even rank of the same line.